A guide bar is disclosed in U.S. Pat. No. 3,995,370 wherein guide plates are mounted in the region of the bar tip on each longitudinal side of the guide bar. The guide plates project laterally beyond the guide rails of the guide groove. The radial projection is so provided that the chain links are substantially covered laterally and only the cutting links project beyond the edge of the guide plates. In this way, it is ensured that the penetration depth of the cutting teeth into the wood to be cut is reduced during plunge cutting. The kickback tendency during plunge cutting is intended to thereby be reduced.
In practice, it has been shown that a projection of the fixed guide plates, which is too great, leads to a deterioration of the cutting power and plunge cutting work can be hindered. On the other hand, the projection of the guide plates is, however, to be selected so large that the kickback tendency of the motor-driven chain saw is reduced for plunge cutting work. These two requirements contradict each other and can only be solved by a compromise which is unsatisfactory.
It is an object of the invention to provide a guide bar of the kind described above, which is so improved that the kickback effect is reduced for plunge cutting work while, at the same time, providing a good cutting power.
The guide bar of the invention is for a saw chain of a motor-driven chain saw having a housing, the saw chain including cutting links, lateral connecting links and center drive links pivotally connected to each other via rivets with the drive links having respective rakers formed thereon. The guide bar includes: an elongated planar base body defining an outer periphery wherein a peripheral guide groove is provided for receiving the rakers therein and for guiding the saw chain along the outer periphery; the guide bar having guiding surfaces along the outer periphery for supporting the lateral connecting links and the cutting links and the guiding surfaces being separated from each other by the guide groove; the guide bar having an attachment end at one end thereof for attaching the guide bar to the housing of the chain saw and a direction-changing section at the other end thereof for guiding the saw chain over the outer free end of the guide bar; guide plates mounted on the base body in the direction-changing section and extending radially beyond the guiding surfaces to laterally cover the connecting links and the cutting links of the saw chain; and, the guide plates being configured as rotating guide discs.
It has been shown that a good cutting power is achieved when configuring the guide plates as rotating guide discs and the kickback effect is nonetheless significantly reduced. Depending upon boundary conditions, the kickback angle is significantly reduced compared to conventional guide bars.
Advantageously, the guide discs are driven by the moving saw chain whereby a taking along of the guide discs is provided in the running direction of the saw chain.
It is practical to connect the guide discs so that they rotate with the idler sprocket held in the tip of the guide bar. The saw chain entrains the idler sprocket form tight and the idler sprocket takes along the guide discs in the direction of rotation, for example, via the bearing of the idler sprocket. The direction-changing section is assembled for this purpose from side plates and a bearing for a guide disc is mounted in each side plate.
Preferably, the rotating guide discs have a radius which is so large that the disc edge ends at a slight spacing radially below the cutting roof. In order that there is no hindrance of the cutting action in the region of the cutting tooth, a cutting section of the cutting tooth projects beyond the disc edge or, in the region of the cutting tooth, a cutout is provided in the disc edge which exposes the cutting tooth.